This invention relates to a method and apparatus for holographically discerning an object, using any kind of coherent wave such as electromagnetic wave or sound wave, and more particularly to such a method and apparatus in which some of the coherent waves scattered in all directions by the object are detected at a fixed point for a three-dimensional or holographic discernment of the object.
Holographic techniques have been known as a means for a three-dimensional discernment and visible reconstruction of an object. A coherent wave scattered by the object is made to interfere with a reference coherent wave to produce an interference pattern. A three-dimensional image of the object will result from the interference pattern. Also, the interference pattern can be recorded and stored for the later reconstruction of the three-dimensional image of the object. The interference pattern is generally called a "holograph." In case where a coherent wave in the range of visible rays is used to produce holographs, a photographic film can be advantageously used. However, where a microwave is used to produce holographs, disadvantageously there is no means to record the whole image of the object at the same time as can be done in the recording of the image on a photographic film.
In this connection in producing microwave-holographs there have been hitherto used means to mechanically move a receiving antenna to sweep as broad an area as required in the form of lines or dots. Otherwise, there has been used a two-dimensional array of numerous antennas to cover as broad an area as required, and with this arrangement the outputs of these antennas are sequentially picked up by a proper electronic switching means to construct a spatial interference pattern.
As for the former means to mechanically move a receiving antenna, a complicated mechanism is required, and still disadvantageously it takes much time to produce a single holograph. Therefore, the former method is practically useless. As for the latter means, it requires many antennas units built in the form of array, and from the point of economy it lacks practicality. There has hitherto been no practical method using a microwave to holographically discern an object in a three-dimensional way.
The object of this invention is to provide a method and apparatus using a coherent wave other than visible rays, such as an electromagnetic wave (microwave, or millimeter wave), a sound wave (ultrasonic wave) or a beam of electrons for a three-dimensional discernment of an object.